Distillation of alcohols containing impurities less soluble in water



May 17, 1-949. .1. A. PATTERSON 2,470,222

DISTILLATION OF ALCOHOLS CONTAINING IMPURITIES LESS SOLUBLE IN WATERFiled Aug. 10, 1944 2 Sheets-Sheet l '22 QAFF|NATE- f" v WATEP. ANDOTHER. 016mm \m ulunes 1 EXTQACTOP.

:0 WATER.

Ex-rRAcT L STILL lasmut Ana mourn-nae J. A. PATTERSON DISTILLATION 0FALCOHOLS CONTAINING IMPURITIES LESS SOLUBLE IN WATER Filed Aug. 10,1944

I I I Couoeusea. 55' I Couocnsefl.

2 Sheets -SheeI'. 2

0 II R a 3 I. E II o e5 v 1 O 3 3 I I 'I I I.I I I I l I I I I I l l I II I I I l I I 3 A g A n6 5's 9 3 K I H 35 a JD In 55 5 cl 8 1s I I I I I'I I I c HI III: n $1? P p a 6 l: 5 In 5', 5 O

I In: 2; m 9 Q 3: :32 d :5 EU i 5 i 3 3 John C7. Patterson UnvenborClbborneq Patented May 17, 1949 DISTILLATION OF ALCOHOLS CONTAININGIMPURITIES LESS SOLUBLE IN WATER John A. Patterson, Westfield, N. J.,assignor, by

mesne assignments, to Standard Oil Development Company, a corporation ofDelaware Application August 10, 1944, Serial No. 548,922

10 Claims. (Cl. 202-42) This invention relates to the purification oforganic liquids. The invention relates specially to the removal duringdistillation "of impurities from the monohydric alcohols containing upto about'five carbon atoms in the molecule. This application is acontinuation in part of application Serial No. 423,318, filed December18, 1941 (now abandoned).

In the purification of commercial organic liquids such as the alcoholsproduced by the treatment of olefins with sulfuric acid, the removal ofimpurities from the crude supply must be efiected in a relatively simpleand inexpensive manner. The establishing of such suitable refiningprocedure is beset with many difliculties, especially when theimpurities are of a nature unsuitable as commercial by-products. Theimpurities which normally occur in such organic liquids can be dividedinto two classes: (1) the low boiling, relatively water-insolublematerials consisting mainly of ethers and hydrocarbons; and (2) highboiling, relatively water-insoluble impurties, usually of the nature ofcomplex oxygenand sulfur-containing compounds. The problem is alsopresented of removing the low boiling and high boiling impurities whenan entrainer is employed in an azeotropic dehydration process for forthe organic liquid.

Distillation is generally the easiest and cheapest means of extractingan organic liquid from a crude supply. When the organic liquid forms aconstant boiling mixture with Water, the low boiling impurities andwater in the crude stock are easily removed. first as constituents ofazeotropes which form two phases upon condensation. From the residualmaterial a considerable portion of the organic liquid may ordinarily beobtained -in a high degree of purity. It is, however, generallyimpossible to remove all of the organic liquid from the residue in ahigh degree of purity. As the high boiling impurities are concentratedin the residue, the boiling point of the mixture increases to a point towhich appreciable quantities of such impurities are distilled over withthe product. In addition, it frequently happens that as the temperatureincreases the impurities which contain higher unsaturated compounds suchas the alcohols-and ketones decompose, giving products which impart tothe organic liquid undesirable colors and odors.

When the distillation of the organic liquid is conducted in the presenceof an excess of water, as is generally the case in the purification ofthe lower alcohols, the tendency of the higher boiling impurities todecompose is reduced but the tendency to carry the high boilingimpurities overhead with the pure organic liquid isincreased as a resultof the steam distillation involved. In such cases, it is necessaryto'withdraw the impurities either as residue or as a side stream with ahigh content of the product organic liquid.

In the prior art, the high boiling impurities obtained in thepurification of many organic liquids have been removed from distillationsystems in considerable dilution. The removal of the impurities fromsuch solutions has usually been effected by solvent extraction, that is,employing a liquid which dissolves either the undesirable impurities orthe desirable organic liquid so that diphase systems are formed. In thismanner, a relative separation of the impurities has been effected. Formost commercial organic liquids the solvent employed in such cases iswater since in the case of lower alcohols the {organic liquid'is solublewhile the impurities are relatively insoluble. The extraction of theconcentrated solution of the impurities with water is usually dificultand frequently unsatisfactory because of the very small differences indensity between the two phases and also because of the tendencies toform emulsified solutions.

It has been found that by adding a concentrated solution of the lowboiling impurities to the concentrated solution of the high boilingimpurities a separation of the high boiling impurities can beadvantageously effected by solvent extraction. It has also been foundthat the high boiling impurities may also be similarly removed from aconcentrated solution of the high boiling impurities when largequantities of water are associated with the organic liquid after theremoval of the low boiling impurities.

When the low boiling impurities are removed as constituents ofazeotropes in the first stage of the distillation, the relativelynon-aqueous phase which normally forms upon condensation has been addedto the concentrated solution of the high boiling impurities. When thecombined solution is treated with a solvent for either the organicliquid or the impurities in which the other is relatively insoluble, ameans satisfactory and inexpensive process has thus been devised for theremoval of easily decomposable impurities obtained in the purification01' many organic liquids. This process has been found particularlyadvantageous in the treatment of residues obtained in the purificationby azeotropic dehydration of the lower. monohydric alcohols and themethyl ketones containing up to six carbon atoms in the molecule:

these two types of compounds have similar.

physicalcharacteristics, especially solubility in water.

Processing according to the invention can be further understood byreading the following description in which the numerals refer to Figures1 and 2. In Figure 1, processing is outlined as can be advantageouslyefiected in batch scale operation, while in Figure 2 processing isoutlined as can be conveniently carried out upon a continuous basis.

Thus, as shown in Figure 1, the crude supply is charged through line iinto still 2 which is connected to distillation column 3 by means ofvapor line 4 and reflux line 5. Heat is supplied to the still 2 by meansof the closed steam coil 6. Distillate material from the distillationcolumn 3 is removed through line 1 to condenser 8. Reflux from thecondenser 8 is passed to the distillation column 3 through line 9. Theinitial distillate is withdrawn through line In to the decanter II inwhich time is allowed for the separationof phases. The relativelyaqueous phase so formed is then passed through line l2 to processequipment not shown for recovery of its alcohol content. The relativelynon-aqueous phase is passed through line 13 in controlled amounts to thestorage vessel l4 and the excess passed.

through line l5. When the initial distillate material has been taken themain distillate of highly purified organic liquid is withdrawn throughline l6, leaving a distillation residue which is removed from still 2through line I I to the storage vessel l4. Thus, in the vessel I 4 thenon-aqueous phase of the initial distillate in controlled amounts ismixed with the distillation residue. The mixture from vessel I 4 is thenpassed through line H! to the countercurrent extractor l9. Wa-

ter is supplied to the extractor l9 through line 20. The water extractis withdrawn from the extractor through line 2| while the raffinate iswithdrawn through line 22.

In Figure 2, a preferred embodiment of carrying out the process of theinvention upon the continuous scale is outlined. In this method ofprocessing the minimum equipment involves the use of two distillationcolumns, mixing equipment and a water-wash column interconnected withthe necessary auxiliary piping equipment.

Thus, into a distillation column 50 the crude supply, as, for example,isopropyl alcohol containing'between about 30 and 50% water, isintroduced through line The column 50 is supplied with open steam as thesource of heat admitted through the base. The column is operated so thatwhen all the low boiling impurities in the crude supply are removed asdistillate material, some alcohol and some water usually as constituentsof azeotropes are also removed. The impurities removed in this mannerthrough line 52 are low boiling hydrocarbons, aldehydes, ketones andethers. The overhead material is passed through condenser 53 and thenceto decanter 54.

Due to the insolubility in water of some of the low boiling compounds,the condensate usually separates in the decanter 54 into two liquidphases, especially when ternary azeotropic mixtures are present. Thepases thus 'formed are usuall separated so that the upper phase y bepartly returned as reflux to the tower through line 55 and the remainderremoved through line 56 to the mixer I2 for combination with the highboiling impurities obtained from the treatment of the distillationresidue. The relatively aqueous phase is removed through line 51 andadded to the crude alcohol supply. When the condensate in the decanter54 does not separate into two phases due to emulsified condition or thepresence of substantial quantities of water-soluble material, the entiredistillat is usually divided into a reflux stream and a stream forpassage to the mixer 12 for combination with the high boiling materials.

The distillation residue from column 50, consisting of alcohol free ofthe low boilin impurities and diluted with Water, is passed through line6| to the column 60. The column 60 is shown as "being heated by means ofa steam connection in the lower part of the column. The column is alsoequipped With an overhead vapor line 62, condenser 63, a reflux drum 64,a reflux line and a product line 66. In some cases there may be aproduct side stream drawoff line 80, in which event the overheadconnections consist of a vapor line connected to a condenser and refluxline 65 only to the column. When the column 60 is heated by means ofopen steam injected into the lower part of the column, additionalequipment includes a side stream line 61, a decanter 68, a return line69 and a bottoms withdrawal line 8|. When closed steam, however, isemployed as the heating means for the tower, this latter series ofauxiliary equipment for withdrawing the side stream is obviated.

When the overhead product consists of alcohol free from the high boilingimpurities, the stream is conducted to a condenser 63 and, aftercondensation, passed to the reflux drum 64. From the reflux drum 64 aportion of the condensate is suppliedas reflux to the column 60 whilethe remainder is removed as product through line 66 and passed tostorage. When open steam is employed as the heating means, thedistillation residue from the bottom of column 60 consists largely ofwater and is removed from the system through line 8|. When closed steamis employed, the distillation residue removed through line 8| consistsessentially of the high boiling impurities in an anhydrous condition.

The high boiling impurities separated from the alcohol when open steamis used in the column 60 are not removed, on account of volatility, inthe overhead stream nor in the distillation residue stream. Thevolatility of these high boiling compounds is lower than that of thealcohol and they are thus retained in the column, but, being insolublein the aqueous residue, are steam distilled and accumulate in the towersome distance below the upper series of plates. At the point in thetower at which the relative concentration of the high boiling impuritiesis at a maximum, separation can be made of a side stream as through line61. Such material is then passed to the decanter 68. Any waterseparating from 6 tained in the purification of methyl ethyl ketone v,as prepared by the dehydration of secondary butyl alcohol.

In the purification treatment on the plant scale the high boilingimpurities in the decanter 68 of ethyl and isopropyl alcohols, it hasbeen found is allowed to settle and is recycled to the column throughline 69 at a plate below that upon which the side stream product wasremoved by means of line 81. The non-aqueous layer in the'decanter 69 isremoved through line II and passed to the mixer 12 to which, aspreviously described, are also passed the low boiling impurities fromthe column 50 through line 56.

The mixture of high and low boiling impurities after mixing in mixer I2is introduced into the wash tower l0 where it is countercurrentlycontacted with water. The water dissolves the alcohol as a dilutesolution which is passed through line I! to the crude alcohol supplyline. The water-insoluble "stream contains the impurities from both ofthe streams supplied to the mixer 12 and only traces of the alcoholand-water.

' When closed steam is used in the column 60, the

high boiling impurities are separated as the distillation residue fromthe column 60 through line 8|. This stream is then passed to equipment12 where it is mixed with the low boiling impurities and then, aspreviously, subsequently etrea --s with water in the tower HI.

A specific illustration of the invention is presented in regard to batchscale treatment in the following comparison of data. These data wereobtained in the treatment of the distillation residue obtained in thepurification of secondary --butyl alcohol alone and when mixed with the3 upper phase material obtained from'the distillate material in theazeotropic dehydration of secondary butyl alcohol. The distillationresidue resulting from the purification of secondary butyl alcoholcontained in this case 64% of secondary o butyl alcohol and 36% ofhighboiling impurities. When this material was extracted with 3 volumesof water in a countercurrent extractor,

and when similar volumes of a mixture of equal volumes of the residueand the upper phase of the distillate material were extracted with 3volumes of water in the same countercurrent extracting equipment, thefollowing comparative data were obtained:

It is to be noted that a higher concentration of alcohol is obtained inthe extract from the extraction of the residue alone.' By suitableadjustment of the water to feed ratio in the extraction of the mixture,as high an alcohol concentration in the extract could be obtained in thelatter case without greatly increasing the alcohol content of therailinate. The only gain in such a case, however, is in the amount ofextract which must be handled to recover the alcohol, since in eithercase essentially the same quantity of alcohol is involved. Similar datamay be obthat processing according to the invention on the continuousscale has produced substantially im proved yields of the ri espectivealcohols. Thus, in the treatment 01 isbpropyl alcohol on plant inoperation, the followingdata have been obtained:

Alcohol Concentrating Column Vol. Per Cent High Boiling Impurities onRespective Plates As a result of such processing, the yield of isopropylalcohol was increased by 16.6% for once 5 through operation over thatpreviously obtained.

With ethyl alcohol the yield was increased by 17.7% by means of asimilar operational improvement.

The method of the invention is applicable to the 30 purification of avariety of commercial organic liquids. The principal feature of theinvention is in regard to the obtaining of higher yields ofthe liquidundergoing purificationdue to the facility of separation of otherwisediflicultly separable im- 5 purities. This separation may be caused, asillustrated in the previous description of the invention, by the mixingof two impure streams obtained during the course of the purificationtreatmentor, as previously discussed, by the mixing of merely the impurestream with an extraneous liquid to obtain the separation between theimpurities and the desired liquid. The method of the invention isparticularly applicable, however, to the lower monohydric alcohols,ketones and organic liquids of similar physical characteristics,especially solubility in water.

What is claimed is:

1. An improved process for the purification of r a crude alcoholcontaining from one to six carbon atoms in the molecule prepared fromolefins by hydrolysis, which comprises distilling the crude alcohol,separating a light distillate fraction containing any light boilingimpurities and water in said crude alcohol, a heavier fractioncontaining a major amount of the alcohol undergoing purification and ahigh boiling fraction containing the alcohol undergoing purification andany high boiling impurities, combining said fraction containing any highboiling impurities into solution with a portion of said fractioncontaining any low boiling impurities and treating said solution withwater to extract the alcohol.

2. A process according to claim 1 in which the extraction of saidsolution is eifected countercurrently.

3. A process according to claim 1 in which the portion of the lowboiling'distillate fraction combined with the fraction containing anyhigh boiling impurities is decanted asa non-aqueous phase from waterpresent in said fraction containing low boiling impurities.

4. A process according to claim 1 in which an aqueous alcoholic extractobtained by extraction from said solution is admixed with crude alcoholbeing distilled.

5. A process according to claim 1 in which the alcohol is ethyl alcohol.

6. A process according to claim 1 in which the alcohol is isopropylalcohol.

7. A process according to claim 1 in which the alcohol is secondarybutyl alcohol.

8. An improved process for the purification of secondary butyl alcoholprepared by the treatment of normal butylenes with sulfuric acid whichcomprises heating the crude supply to remove as initial distillate amixture comprising water and low boiling relatively water-insolublecompounds, then the main distillate of relatively pure secondary butylalcohol, leaving a distillation residue consisting essentially of highboiling compounds and secondary butyl alcohol, allowing the initialdistillate material to separate into phases, adding the relativelynon-aqueous phase to the distillation residue, extracting the mixture soobtained with water, adding the aqueous solution thus obtained to therelatively aqueous phase separation obtained from the initial distillatematerial and recovering from this mixture the secondary butyl alcohol.

9. An improved process for purifying an oxygen-containing organiccompound having substantial solubility in water, said compound being ina crude aqueous liquid mixture contaminated by organic impurities havingless solubility in water, which comprises distilling from said mixture alow boiling distillate of said compound with water and impurities in adistillation zone, combining a water immiscible organic liquid into asolution with said impurities of the distillate, extracting the compoundto be purified from said solution with water, returning the resultingwater extract from said solution to said distillation zone, andwithdrawing from said distillation zone a fraction of the compound to bepurified.

10. An improved process for purifying an oxygen-containing organiccompound having substantial solubility in water, said compound being ina crude aqueous liquid mixture contaminated by organic impurities havingless solubility in water with both lower and higher volatility than saidcompound to bev purified in said liquid mixture, which comprisesdistilling from said crude liquid mixture a low boiling distillate oithecompound with water and of the compound with impurities of highvolatility, and a high boiling distillate of said compound to bepurified, and leaving a residual fraction of said crude liquid mixturecontaining a portion of the compound to be purified with impurities oflower volatility and low water solubility, combining impurities of saidresidual fraction into a solution with a water immiscible liquidsolvent, extracting remaining organic compound to be purified from saidsolution with water and adding the resulting water extract to the crudemixture being distilled.

JOHN A. PATTERSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,389,852 Barbet Sept. 6, 1921-2,017,067 Kraft Oct. 15, 1935 2,080,064 Roelfsema May 11, 1937 2,198,651Bludworth Apr. 30, 1940 2,238,016 Downey Apr. 8, 1941 2,317,758 GuinotApr. 27, 1943 2,324,755 Beamer July 20, 1943

